1. Field of the Invention
The present invention relates to improvements in instruments and methods for performing near infrared quantitative analysis to determine percent fat in a body.
2. Description of the Background Art
It has long been known that obesity reduces longevity, and recent studies have demonstrated that high percentage of body fat is an independent health risk factor as a cause of heart attack, stroke, diabetes and other disabling diseases. (Stroke et al, Metabolic Complication of Human Obesities; Elsevier Science Publishers, B.V. (Biomedical Division); J. Vague et al, eds.; pp. 49-57 [1985]).
For the above reasons, several techniques have been developed to determine percent body fat, including recent techniques based USDA research that demonstrates that "near-infrared light interactance" can provide the basis for measurement of percent body fat (Conway et al, The American Journal of Clinical Nutrition 40:1123-1130 [1984]).
Near-infrared light interactance technology disclosed in U.S. Pat. No. 4,633,087 to Rosenthal et al has recently been utilized in a commercial instrument for measurement of body composition, i.e., percent fat in the human body. However, because of the cost required to manufacture an instrument that utilizes this technology, the majority of purchasers are health clubs, medical centers and sports teams, with only a very small percentage of buyers being individual consumers.
Taking full advantage of the technology disclosed in U.S. Pat. No. 4,633,087 requires the measurement of more than one wavelength in the near-infrared spectrum. The reason for this is that what is being measured is the change in slope of the absorption curve, with the slope being defined as the difference in optical absorption at two defined wavelengths.
For the following reasons, the cost of utilizing the technology described in U.S. Pat. No. 4,633,087 remains high even when utilizing inexpensive infrared emitting diodes (IREDs) as the near-infrared source:
(1) The use of two IREDs are preferred for each of two wavelengths being measured, and the more IREDs that are used, the greater the expense.
(2) An electronic means for turning on and off each pair of IREDs in a sequential fashion and keeping them on for a predetermined length of time is required.
(3) Circuitry is required that allows the output of the pairs of IREDs to be adjusted so that they have equal energies when measuring a neutral sample.
(4) Computation circuitry is required that must not only discriminate between two pairs of IREDs, but also perform a multiple regression calculation.
(5) Instrument display capability is required that has the ability to read-out each of the two pairs of IREDs, as well as the final percent fat.
(6) The instrument must also have the ability of entering a multiple number of constants because of the multi-term linear regression equation utilized.
In addition to each of the items discussed above, a major element in the production cost of current near-infrared analysis instruments is the need to calibrate each production unit against a series of known samples via multiple linear regression analyses. These calibration steps are labor intensive and their elimination would enable great reductions in the cost of producing such instruments.
In view of the costs required in providing known devices for measuring body fat content, there remains a need in the art for improved and less expensive devices for measuring percent body fat.